2-Oxazoline based photo-responsive azo-polymers. Synthesis, characterization and isomerization kinetics

Biocompatible, porous hydrogels composed of aliphatic polyesters and poly(2-isopropenyl-2-oxazoline). Their application as scaffolds for bone tissue regeneration

In this study, porous networks were efficiently prepared by crosslinking hydrophilic poly(2-isopropenyl-2-oxazoline) (PiPOx) with dicarboxylic polyesters (HOOC-PLA-COOH or HOOC-PCL-COOH) in the presence of sodium chloride as a water-soluble porogen. Importantly, by using a relatively simple synthetic protocol, the resulting spongy materials were freely formed to the desired size and shape while maintaining stable dimensions. According to the SEM data, the porous 3D structure can be altered by the pore dimensions, which are dependent on the porogen crystal size. After porosity characterization, the mechanical properties were also evaluated via uniaxial compression and tensile tests. The porous networks formed hydrogels with a high water absorption capacity. Finally, after showing cytocompatibility by the MTT assay, we also demonstrated the applicability of the porous hydrogels as scaffolds for cell cultivation. The presented results suggest that this type of hydrogels is a promising material for tissue engineering.

Cytotoxicity and Bioimmunological Activity of Poly(2-Isopropenyl-2-oxazoline) Conjugates with Ibuprofen Using 3D Reconstructed Tissue Models

Poly(2-isopropenyl-2-oxazoline) (PIPOx) represents a universal polymer platform with pendant 2-oxazoline groups, allowing the preparation of biomaterials for various biomedical applications. However, there is a lack of information on PIPOx concerning the effect of molar mass (Mn) on cytotoxicity and bioimmunological properties. Here, aqueous copper(0)-mediated reversible-deactivation radical polymerization (Cu0-RDPR) was used for the preparation of PIPOx with defined Mn and low dispersity. PIPOx of different Mn are used for the synthesis of conjugates with ibuprofen (5 mol %), the nonsteroidal anti-inflammatory drug. The release of ibuprofen at 37 °C and different pH values is monitored using high-performance liquid chromatography, where the rate of drug release increases with increasing pH and lower Mn. In vitro cytotoxicity and bioimmunological properties of PIPOx and drug conjugates are studied using 3D reconstructed tissue models of the human epidermis and intestinal epithelium. We demonstrate low cytotoxicity of PIPOx and conjugates with different Mn values on both 3D tissue models.

Cationic amino-acid functionalized polymethacrylamide vectors for siRNA transfection based on modification of poly(2-isopropenyl-2-oxazoline)

Poly(2-isopropenyl-2-oxazoline) (PiPOx) is a functional polymer showing great potential for the development of smart biomaterials. The straightforward synthesis and post-polymerization functionalization of PiPOx offers many opportunities for tailoring the properties of the polymer towards biomaterials. In this study we report for the first time PiPOx-based cationic charged polymethacrylamides with amino acid side chains that can complex siRNA and promote transfection in vitro. Therefore, PiPOx was fully modified via ring opening addition reactions with the carboxylic acid groups of a series of N-Boc-L-amino acids and their reaction kinetics were investigated. Based on the determined kinetic constants, another series of PiPOx-based copolymers with balanced hydrophilic/hydrophobic content of N-Boc-L-amino acids were obtained via one-pot modification reaction with two different N-Boc-L-amino acids. The N-Boc protected homopolymers and related copolymers were deprotected to obtain (co)polymers with the targeted side chain cationic charged units. The (co)polymers' structures were fully investigated via FT-IR and 1H NMR spectroscopy, size exclusion chromatography (SEC), and TGA-DSC-MS analysis. The polarimetry measurements revealed that the homopolymers retain their chiroptical properties after post-modification, and a sign inversion is noticed from (L) N-Boc-protected analogues to (D) for the TFA cationic charged homopolymers. Generally, cationically charged homopolymers with hydrophilic amino acids on the side chain showed efficient complexation of siRNA, but poor transfection while cationic copolymers having both tryptophan and valine or proline side chains revealed moderate siRNA binding, high transfection efficiency (> 90% of the cells) and potent gene silencing with IC50 values down to 5.5 nM. Particularly, these cationic copolymers showed higher gene silencing potency as compared to the commercial JetPRIME® reference, without reducing cell viability in the concentration range used for transfection, making this a very interesting system for in vitro siRNA transfection.

Covalent segmented polymer networks composed of poly(2-isopropenyl-2-oxazoline) and selected aliphatic polyesters: designing biocompatible amphiphilic materials containing degradable blocks

To promote facile and efficient synthesis of segmented covalent networks, we developed a cross-linking process with reactive polymeric components in a system without catalysts or side products. To achieve the direct formation of amphiphilic networks, an addition reaction was performed between the polyesters containing carboxyl terminal groups with pendant groups distributed along poly(2-isopropenyl-2-oxazoline) chains. Covalent cross-linking was achieved from predetermined amounts of components dissolved in DMSO at 140 °C. To tune the properties of the resulting networks, the composition and length of the polyester segments and the degree of cross-linking were changed in the feed. The chemical structure of the networks was characterized using Fourier transform infrared-attenuated total reflection spectroscopy and 13C magic-angle spinning NMR. The swelling ability of the formed networks was investigated in aqueous and organic media. Moreover, mechanical properties were tested during uniaxial compression. The cytocompatibility of the scaffolds was confirmed by MTT assay. Through the results obtained, the first report describing the cross-linking of polyesters on hydrophilic PiPOx was provided to prepare new, biocompatible materials with tuneable properties that are promising for potential biomedical applications.

Advances and opportunities in the exciting world of azobenzenes

Azobenzenes are archetypal molecules that have a central role in fundamental and applied research. Over the course of almost two centuries, the area of azobenzenes has witnessed great achievements; azobenzenes have evolved from simple dyes to 'little engines' and have become ubiquitous in many aspects of our lives, ranging from textiles, cosmetics, food and medicine to energy and photonics. Despite their long history, azobenzenes continue to arouse academic interest, while being intensively produced for industrial purposes, owing to their rich chemistry, versatile and straightforward design, robust photoswitching process and biodegradability. The development of azobenzenes has stimulated the production of new coloured and light-responsive materials with various applications, and their use continues to expand towards new high-tech applications. In this Review, we highlight the latest achievements in the synthesis of red-light-responsive azobenzenes and the emerging application areas of photopharmacology, photoswitchable adhesives and biodegradable materials for drug delivery. We show how the synthetic versatility and adaptive properties of azobenzenes continue to inspire new research directions, with limits imposed only by one's imagination.

Contrasting Photo-Switching Rates in Azobenzene Derivatives: How the Nature of the Substituent Plays a Role

A molecular design approach was used to create asymmetrical visible light-triggered azo-derivatives that can be good candidates for polymer functionalization. The specific electron-donor substituted molecules were characterized and studied by means of NMR analyses and UV-visible spectroscopy, comparing the results with Time Dependent Density Functional (TD-DFT) calculations. A slow rate of isomerization (ki = 1.5 × 10-4 s-1) was discovered for 4-((2-hydroxy-5methylphenyl) diazenyl)-3-methoxybenzoic acid (AZO1). By methylating this moiety, it was possible to unlock the isomerization mechanism for the second molecule, methyl 3-methoxy-4-((2-methoxy-5-methylphenyl) diazenyl)benzoate (AZO2), reaching promising isomerization rates with visible light irradiation in different solvents. It was discovered that this rate was heightened by one order of magnitude (ki = 3.1 × 10-3 s-1) for AZO2. A computational analysis using density functional (DFT/PBE0) and wavefunction (QD-NEVPT2) methodologies provided insight into the photodynamics of these systems. Both molecules require excitation to the second (S2) excited state situated in the visible region to initiate the isomerization. Two classic mechanisms were considered, namely rotation and inversion, with the former being energetically more favorable. These azo-derivatives show potential that paves the way for future applications as building blocks of functional polymers. Likewise, they could be really effective for the modification of existing commercial polymers, thus transferring their stimuli responsive properties to polymeric bulky structures, converting them into smart materials.

Classifications, properties, recent synthesis and applications of azo dyes

In this work, we have presented a very detailed review of the different classification of azo dyes as a function of the number of azo groups and the appropriate functional groups. Then we pointed out some chemical properties of these dyes such as reactivity, isomerization and tautomerism and listed. In the following, we have summarized some recent syntheses of azo dyes and the mechanism of azo dye/polymer conjugation. Finally, we indicate the principle of Gewald's reaction and its application to the synthesis of new azo dyes.

Poly(2-isopropenyl-2-oxazoline) – a structural analogue to poly(vinyl azlactone) with Orthogonal Reactivity

A modular copolymer platform based on two oxazole derivatives is presented. Post-polymerisation modifications revealed the potential to selectively modify the individual side groups, providing access to functional copolymer libraries in the future.

Poly(2-isopropenyl-2-oxazoline) as a versatile platform towards thermoresponsive copolymers

Thermoresponsive (co)polymers with LCST behavior based on a well-defined PiPOx scaffold showing high versatility in tuning up the T_CP as well as the interval of response.